linux-kernel - Re: [PATCH] watchdog: s3c2410_wdt: Only register for cpufreq on CPU_FREQ

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Date:	Tue, 26 Nov 2013 00:27:41 +0100
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Doug Anderson <dianders@...omium.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	Leela Krishna Amudala <l.krishna@...sung.com>,
	Olof Johansson <olof@...om.net>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Ben Dooks <ben-linux@...ff.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-watchdog@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog: s3c2410_wdt: Only register for cpufreq on CPU_FREQ_S3C24XX

On Monday 25 of November 2013 15:23:27 Guenter Roeck wrote:
> On 11/25/2013 02:55 PM, Doug Anderson wrote:
> > On modern SoCs the watchdog timer is parented on a clock that doesn't
> > change every time we have a cpufreq change.  That means we don't need
> > to constantly adjust the watchdog timer, so avoid registering for and
> > dealing with cpufreq transitions unless we've actually got
> > CPU_FREQ_S3C24XX defined.
> >
> > Note that this is more than just an optimization.  The s3c2410
> > watchdog driver actually pats the watchdog on every CPU frequency
> > change.  On modern systems these happen many times per second (even in
> > a system where "nothing" is happening).  That effectively makes any
> > userspace watchdog program useless (the watchdog is constantly patted
> > by the kernel).  If we need CPU_FREQ_S3C24XX defined on a
> > multiplatform kernel we'll need to make sure that kernel supports
> > common clock and change this to user common clock framework.
> >
> > Signed-off-by: Doug Anderson <dianders@...omium.org>
> > ---
> >   drivers/watchdog/s3c2410_wdt.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
> > index 7d8fd04..4980f84 100644
> > --- a/drivers/watchdog/s3c2410_wdt.c
> > +++ b/drivers/watchdog/s3c2410_wdt.c
> > @@ -264,7 +264,7 @@ static irqreturn_t s3c2410wdt_irq(int irqno, void *param)
> >   	return IRQ_HANDLED;
> >   }
> >
> > -#ifdef CONFIG_CPU_FREQ
> > +#ifdef CONFIG_CPU_FREQ_S3C24XX
> >
> Where is the CPU_FREQ_S3C24XX configuration option defined ? I don't see it
> in the current upstream kernel, so it appears that this depends on some
> out-of-tree changes.

Seems like it got renamed to ARM_S3C24XX_CPUFREQ by f023f8dd59.

Best regards,
Tomasz

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